1. Field of the Invention
The present invention relates to an image projection apparatus.
2. Description of the Related Art
Conventionally, an image projection apparatus uses an image modulation element, such a liquid crystal element, to modulate—in accordance with an image signal—the polarization direction of linearly polarized light incident thereupon to obtain a high contrast image. One of the challenges in this type of image projection apparatus is to optimize the use of light with a first linear polarization direction while blocking light with a second (orthogonal) polarization direction without diminishing the quality of the image. To that end, various solutions have been proposed. For example, in a conventional image projection apparatus, a polarizing plate is arranged between a dichroic mirror (color separation element) and a polarizing beam splitter that analyzes the light modulated by the image modulation element. Purportedly, this arrangement is used to obtain an image having a sufficiently high contrast.
U.S. Pat. No. 6,183,090 to Nakanishi et al. (“Nakanishi”) discusses an image projection apparatus in which light from a light source is guided to an image modulation element via a polarizing beam splitter. In the image projection apparatus disclosed by Nakanishi, the polarization degree of the light incident on the image modulation element is increased by arranging a polarizing plate on the incident side of the polarizing beam splitter. More specifically, since S polarized light is incident on the polarizing beam splitter which guides the light in the red, green, and blue wavelength bands to the image modulation element, the polarizing plate which absorbs or reflects P polarized light is arranged on the incident side of each polarizing beam splitter, so that only S polarized light is transmitted.
However, since the polarizing plate absorbs also reflects a part of the polarized light that needs to be transmitted, the amount of light that passes through the polarizing plate decreases. Thus, there is the problem that although high contrast may be obtained by providing the polarizing plate, the projected image is darker than when the polarizing plate is not inserted on the incident side of each polarizing beam splitter.